Hot melt adhesives are applied to a substrate while in a molten state and cooled to harden the adhesive layer. The hot melt adhesives are commonly used to seal packages such as cardboard cases, trays and cartons. Depending on the environmental and transportation conditions, some packages require the hot melt adhesive to have high heat resistance and low cold temperature performance. Typically, conventional hot melt adhesive exhibit strong bonds at either high or low temperature, but not at both ends of the temperature spectra. Thus, depending on the desired needs of the packages or the environmental conditions, different or multiple adhesives must be used, leading to longer down-times in the manufacturing process.
Ethylene vinyl acetate (EVA) with high vinyl acetate content is used widely in the hot melt adhesives for case and carton sealing for a number of reasons. The high vinyl acetate content of the polymer forms strong adhesion to polar cellulosic substrates; however, the high vinyl acetate content EVA polymers are costly and lead to poor adhesion at either low or high temperature spectra.
Low temperature adhesion may be improved for hot melt adhesives by utilizing low glass transition temperature polymers and/or low melting point waxes and tackifiers. This improvement occurs at the expense of high temperature performance of the adhesive.
There is a need in the art for hot melt adhesives that extends the service temperature windows at both ends of the spectra. The current invention fulfills this need.